The core pathology component provides services yielding data for all the program projects. Beyond the usual activities of a diagnostic pathology service this group provides a large body of essential data which is available to all investigators on this program project. This group also coordinates the extensive specimen collection on autopsies and biopsies needed to carry out the research proposals in this program project. These include the preparation of frozen tissues and tissue culture specimens, support in immunology and virology by immunohistochemical and DNA hybridization techniques and a variety of histological methods. Many non-routine studies are performed. Major collaborative research projects are a) graft-versus-host disease (Project II), b) viral infection (Project III), c) venocclusive disease (Project X. H), and d) hematopathology (Project VIII).